40207_11 - PARTICULATE FILLERS H arry 11 s. Kat2 11.1...

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PARTICULATE FILLERS 11 Harry s. Kat2 11.1 INTRODUCTION The preceding chapters of this handbook dis- cussed fiber reinforcements. Fibers play an important role as the outstanding means for obtaining great increases in the strength and modulus of the matrix material. The focus of attention on fiber reinforcements has usually blinded potential end users of composite materials to the many beneficial uses of non- fibrous, or particulate, fillers. However, industrial experts are now becoming more aware of these benefits and there will undoubtedly be increased particulate filler usage in future polymers, ceramics and met- als. Particulate fillers can provide improved materials, as compared with the unfilled matrix and can also be synergistic with a fiber reinforcement to further improve the system performance. A fiber may be described as a particle with a length-to-diameter ratio of greater than 10 to 1. A particulate filler may be described as a non fibrous solid that fits the definition given in the Compilation of ASTM Standard Definitions, ‘a solid compounding material, usually in finely divided form, which may be added in relatively high proportions to a poly- mer for technical or economic reasons.’ This chapter will not include additives such as antioxidants or internal mold release agents, which serve important compounding func- tions, but are used at low levels, usually below Handbook of Composites. Edited by S.T. Peters. Published in 1998 by Chapman & Hall, London. ISBN 0 412 54020 7 2 wt.% in the composite material. The only exception is the inclusion of a brief discussion of coupling agents, which serve an important function in achieving optimum physical prop- erties in particulate filler composites. There are many good reasons for using par- ticulate fillers in plastic, metal or ceramic matrices, in addition to the obvious usual reduction in cost of the final product. In the case of plastics, the addition of fillers provides a reduction of shrinkage during the cure of a thermoset polymer system or the injection molding of a thermoplastic resin. This reduced shrinkage results in important benefits such as avoidance of the warpage or cracking that may occur, especially in the case of large molded parts. Also, the thermal conductivities of mineral fillers are usually in the order of ten times greater than the thermal conductivity of polymers. Therefore, the filled polymer has a much greater thermal conductivity than the unfilled resin. This provides an important advantage in processes such as injection mold- ing, where the cycle time is often determined by the time to cool the part in the mold. The faster cooling rate of the filled plastic will pro- vide cost savings due to the faster cycle time.
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This note was uploaded on 03/16/2010 for the course MECHANICAL ME765401 taught by Professor Prof.sulis during the Spring '10 term at Institut Teknologi Bandung.

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40207_11 - PARTICULATE FILLERS H arry 11 s. Kat2 11.1...

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